Talk by James Blackmon from San Francisco State University. Given at the Redwood Center for Theoretical Neuroscience at UC Berkeley.
Conscious minds are sometimes revealed upon the permanent or even temporary loss of a functioning brain hemisphere. We know this because of two medical procedures which have existed for many decades: the hemispherectomy and the Wada test. In an anatomical hemispherectomy, one hemisphere is removed from the cranium and discarded, yet survivors of this radical procedure can emerge exhibiting a memory of who they are and what it was once like to have lived with that other hemisphere. In a Wada test, hemispheres are alternately anesthetized while the other hemisphere performs language and memory tasks for the sake of preoperative diagnosis. Again, some memories appear to persist through the procedure's transitions, and it is not unusual for patients to later report what it was like to be momentarily unable to name an object. Short of other-minds skepticism, we have every reason (medical, scientific, and practical) to consider patients under these conditions to be conscious. And yet that which survives the loss of the left hemisphere is obviously not that which would have survived the loss of the right. I argue that patient testimony and behavior suggests that there are phenomenally conscious experiences of losing (and, in the case of the Wada test, regaining) functional interaction with another hemisphere. Moreover, I argue that the relevant medical facts are best explained by the postulate that typical healthy brains host many conscious entities--some of them deserving to be called minds.